Arrow Heights Astroimaging Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arrow Heights Astroimaging Observatory clear sky chart from 2005-11-06 to 2024-04-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 7% 3 5% 5% 3 5% 5% 5% 7% 41%	78911
	Night	14% 8% 3 6% 5% 3 4 4 5% 6% 42%	81272
Transparency	Day	40% 7% 12% 23% 15% 2	78620
	Night	42% 6% 11% 23% 16% 3	81085
Seeing	Day	15% 10% 25% 27% 18% 5%	14718
	Night	16% 9% 29% 31% 14% 1	24742

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 12% 5% 10% 7% 4 5% 5% 6% 7% 29%	2527
	11th to 20th	Day	13% 8% 4 7% 8% 6% 6% 5% 5% 6% 32%	2726
	21st to end	Day	21% 18% 5% 7% 5% 3 3 3 3 5% 27%	3135
February	1st to 10th	Day	16% 9% 5% 8% 5% 3 5% 5% 4 7% 32%	1710
	11th to 20th	Day	15% 8% 4 7% 6% 3 4 4 5% 6% 38%	1827
	21st to end	Day	15% 10% 4 7% 5% 2 4 4 4 7% 38%	1570
March	1st to 10th	Day	15% 9% 3 6% 5% 3 3 5% 4 6% 41%	1925
	11th to 20th	Day	18% 10% 3 5% 6% 3 4 4 5% 6% 36%	2090
	21st to end	Day	19% 11% 5% 7% 6% 3 5% 5% 5% 6% 29%	2419
April	1st to 10th	Day	12% 7% 2 6% 6% 3 5% 5% 6% 7% 42%	2184
	11th to 20th	Day	17% 8% 3 5% 5% 3 5% 4 4 6% 41%	2134
	21st to end	Day	17% 6% 3 6% 6% 3 4 5% 4 7% 37%	2160
May	1st to 10th	Day	17% 6% 2 6% 6% 3 6% 5% 6% 7% 37%	2214
	11th to 20th	Day	16% 6% 3 5% 4 3 5% 5% 6% 8% 40%	2452
	21st to end	Day	10% 6% 2 5% 7% 4 7% 6% 7% 9% 37%	2725
June	1st to 10th	Day	8% 5% 2 4 4 3 5% 6% 6% 8% 48%	2520
	11th to 20th	Day	8% 3 2 4 4 3 5% 6% 6% 9% 49%	2520
	21st to end	Day	5% 3 3 4 5% 3 5% 7% 8% 11% 46%	2520
July	1st to 10th	Day	9% 3 2 4 5% 4 6% 6% 8% 10% 43%	2520
	11th to 20th	Day	5% 3 2 3 4 3 5% 7% 7% 10% 51%	2520
	21st to end	Day	8% 5% 2 4 5% 3 5% 6% 6% 8% 47%	2615
August	1st to 10th	Day	7% 4 3 4 5% 4 6% 7% 8% 10% 42%	2324
	11th to 20th	Day	9% 5% 2 6% 6% 4 5% 6% 7% 10% 40%	2125
	21st to end	Day	8% 5% 3 4 4 3 5% 5% 5% 9% 50%	2376
September	1st to 10th	Day	14% 4 2 4 4 2 4 4 5% 8% 49%	2160
	11th to 20th	Day	9% 5% 2 4 5% 3 4 4 6% 9% 50%	2138
	21st to end	Day	7% 5% 2 4 4 3 5% 4 5% 8% 54%	1976
October	1st to 10th	Day	10% 5% 2 4 5% 3 3 3 4 7% 54%	1800
	11th to 20th	Day	15% 6% 2 4 4 2 2 4 3 7% 51%	1800
	21st to end	Day	19% 7% 3 3 4 3 3 3 3 5% 46%	1960
November	1st to 10th	Day	10% 5% 3 4 4 3 4 4 4 6% 55%	1672
	11th to 20th	Day	15% 7% 2 4 5% 3 3 3 5% 6% 47%	1710
	21st to end	Day	16% 10% 4 6% 5% 2 4 4 4 6% 41%	1636
December	1st to 10th	Day	13% 12% 3 6% 5% 2 4 4 4 7% 39%	1520
	11th to 20th	Day	14% 10% 4 6% 5% 3 4 4 5% 7% 38%	1918
	21st to end	Day	21% 14% 5% 7% 6% 3 4 3 5% 6% 25%	2783
January	1st to 10th	Night	14% 10% 6% 9% 5% 3 4 4 4 5% 34%	4428
	11th to 20th	Night	13% 11% 4 10% 7% 4 7% 4 4 5% 31%	4242
	21st to end	Night	24% 16% 5% 7% 5% 2 3 3 4 6% 26%	4532
February	1st to 10th	Night	16% 11% 5% 7% 6% 3 4 4 5% 6% 34%	2470
	11th to 20th	Night	15% 7% 4 8% 5% 2 4 4 3 6% 41%	2237
	21st to end	Night	15% 11% 3 7% 5% 2 4 3 4 5% 40%	1884
March	1st to 10th	Night	17% 10% 3 4 5% 2 4 3 4 5% 43%	2271
	11th to 20th	Night	18% 8% 3 6% 4 3 4 5% 5% 6% 39%	2090
	21st to end	Night	19% 10% 4 7% 6% 3 5% 3 5% 6% 33%	2178
April	1st to 10th	Night	12% 7% 2 6% 5% 3 3 4 4 7% 47%	1820
	11th to 20th	Night	13% 7% 3 4 5% 3 4 4 5% 8% 44%	1775
	21st to end	Night	19% 7% 3 6% 5% 2 4 3 4 7% 40%	1800
May	1st to 10th	Night	15% 6% 3 5% 4 2 4 5% 5% 8% 43%	1746
	11th to 20th	Night	16% 7% 3 5% 4 2 4 3 5% 7% 44%	1439
	21st to end	Night	9% 5% 3 6% 6% 3 5% 6% 6% 10% 41%	1551
June	1st to 10th	Night	8% 4 3 4 5% 3 4 4 7% 9% 50%	1440
	11th to 20th	Night	5% 3 2 4 3 3 4 5% 6% 10% 54%	1440
	21st to end	Night	4 4 2 4 4 3 4 6% 5% 11% 54%	1440
July	1st to 10th	Night	9% 3 2 4 4 2 5% 5% 7% 9% 51%	1440
	11th to 20th	Night	5% 3 2 4 4 3 5% 5% 5% 9% 56%	1440
	21st to end	Night	6% 5% 2 6% 5% 4 4 5% 6% 10% 49%	1700
August	1st to 10th	Night	7% 4 1 4 4 3 5% 6% 6% 8% 52%	1615
	11th to 20th	Night	6% 5% 2 5% 5% 3 5% 6% 6% 7% 50%	1776
	21st to end	Night	5% 3 2 4 4 3 5% 4 6% 8% 57%	1980
September	1st to 10th	Night	12% 4 2 4 4 3 4 4 4 7% 52%	1800
	11th to 20th	Night	8% 5% 2 5% 5% 3 4 4 5% 7% 52%	1804
	21st to end	Night	8% 3 2 4 5% 3 4 5% 4 6% 56%	1980
October	1st to 10th	Night	9% 5% 2 4 3 2 3 5% 4 6% 57%	2160
	11th to 20th	Night	14% 5% 2 4 4 2 3 4 5% 7% 51%	2160
	21st to end	Night	19% 7% 2 5% 3 2 4 3 4 4 47%	2394
November	1st to 10th	Night	10% 5% 2 3 5% 2 4 4 5% 5% 56%	2406
	11th to 20th	Night	14% 5% 2 5% 4 3 4 4 4 6% 49%	2470
	21st to end	Night	18% 8% 3 5% 3 2 3 3 4 6% 44%	2541
December	1st to 10th	Night	15% 10% 4 6% 5% 3 4 4 5% 7% 35%	2660
	11th to 20th	Night	16% 9% 4 6% 5% 3 4 3 4 6% 41%	3279
	21st to end	Night	19% 18% 5% 9% 6% 4 4 4 4 4 23%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	49% 9% 11% 22% 8% 1	2528
	11th to 20th	Day	48% 8% 14% 20% 11%	2726
	21st to end	Day	59% 5% 9% 16% 10% 1	3135
February	1st to 10th	Day	51% 6% 11% 21% 10% 1	1710
	11th to 20th	Day	47% 6% 11% 20% 14% 3	1837
	21st to end	Day	46% 6% 9% 22% 14% 4	1570
March	1st to 10th	Day	45% 5% 9% 23% 15% 2	1925
	11th to 20th	Day	50% 6% 11% 18% 13% 2	2090
	21st to end	Day	55% 7% 12% 18% 8% 1	2419
April	1st to 10th	Day	40% 6% 12% 25% 16% 1	2184
	11th to 20th	Day	45% 5% 11% 22% 13% 3	2134
	21st to end	Day	46% 8% 11% 22% 13% 1	2160
May	1st to 10th	Day	46% 8% 14% 22% 10% 1	2214
	11th to 20th	Day	41% 9% 12% 22% 14% 1	2456
	21st to end	Day	40% 10% 15% 20% 12% 2	2725
June	1st to 10th	Day	33% 8% 14% 26% 17% 2	2520
	11th to 20th	Day	29% 8% 14% 23% 23% 3	2520
	21st to end	Day	28% 10% 18% 23% 15% 5%	2520
July	1st to 10th	Day	32% 9% 16% 25% 13% 4	2451
	11th to 20th	Day	25% 9% 16% 27% 20% 3	2445
	21st to end	Day	32% 8% 13% 29% 16% 2	2470
August	1st to 10th	Day	33% 10% 14% 27% 16%	2310
	11th to 20th	Day	36% 9% 15% 26% 13% 1	2125
	21st to end	Day	29% 8% 14% 24% 19% 5%	2376
September	1st to 10th	Day	33% 6% 11% 27% 18% 5%	2160
	11th to 20th	Day	31% 6% 10% 25% 25% 3	2138
	21st to end	Day	29% 5% 9% 29% 24% 3	1976
October	1st to 10th	Day	31% 5% 10% 25% 25% 4	1800
	11th to 20th	Day	35% 4 10% 24% 22% 5%	1800
	21st to end	Day	41% 4 9% 26% 16% 4	1960
November	1st to 10th	Day	32% 5% 12% 26% 20% 5%	1672
	11th to 20th	Day	38% 5% 10% 23% 20% 5%	1710
	21st to end	Day	46% 5% 9% 25% 14%	1636
December	1st to 10th	Day	44% 7% 12% 25% 12%	1520
	11th to 20th	Day	46% 6% 11% 23% 12% 2	1915
	21st to end	Day	59% 7% 11% 14% 8% 1	2783
January	1st to 10th	Night	50% 7% 11% 23% 9% 1	4428
	11th to 20th	Night	55% 8% 9% 19% 9% 1	4242
	21st to end	Night	59% 5% 10% 18% 7% 1	4532
February	1st to 10th	Night	52% 5% 10% 20% 12% 1	2470
	11th to 20th	Night	45% 5% 10% 21% 17% 2	2238
	21st to end	Night	47% 5% 11% 21% 13% 4	1884
March	1st to 10th	Night	45% 5% 8% 23% 16% 2	2271
	11th to 20th	Night	47% 6% 10% 21% 13% 3	2090
	21st to end	Night	53% 6% 12% 20% 9% 1	2178
April	1st to 10th	Night	38% 6% 9% 26% 18% 3	1820
	11th to 20th	Night	39% 5% 11% 23% 18% 4	1775
	21st to end	Night	45% 6% 8% 23% 17% 2	1800
May	1st to 10th	Night	40% 7% 13% 23% 16% 2	1746
	11th to 20th	Night	40% 8% 11% 25% 15% 2	1440
	21st to end	Night	36% 10% 14% 20% 16% 3	1552
June	1st to 10th	Night	30% 7% 15% 26% 18% 3	1440
	11th to 20th	Night	24% 8% 13% 26% 25% 4	1440
	21st to end	Night	23% 9% 16% 27% 18% 6%	1440
July	1st to 10th	Night	30% 8% 14% 29% 15% 5%	1400
	11th to 20th	Night	24% 7% 16% 29% 20% 4	1392
	21st to end	Night	29% 8% 13% 30% 18% 2	1606
August	1st to 10th	Night	26% 9% 15% 32% 15% 2	1605
	11th to 20th	Night	30% 8% 13% 27% 21% 2	1776
	21st to end	Night	25% 7% 15% 25% 23% 5%	1980
September	1st to 10th	Night	32% 6% 10% 24% 22% 7%	1800
	11th to 20th	Night	30% 6% 9% 25% 25% 5%	1804
	21st to end	Night	28% 7% 9% 24% 28% 4	1980
October	1st to 10th	Night	27% 7% 10% 24% 26% 5%	2160
	11th to 20th	Night	32% 5% 8% 28% 20% 7%	2160
	21st to end	Night	41% 5% 9% 21% 21% 4	2394
November	1st to 10th	Night	30% 5% 12% 25% 22% 6%	2406
	11th to 20th	Night	37% 4 9% 25% 21% 4	2470
	21st to end	Night	42% 5% 11% 24% 17% 2	2541
December	1st to 10th	Night	48% 6% 10% 24% 11% 1	2660
	11th to 20th	Night	45% 5% 11% 23% 15% 1	3281
	21st to end	Night	62% 8% 9% 13% 7% 1	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 22% 36% 17% 7% 1	270
	11th to 20th	Day	27% 16% 38% 18% 2	270
	21st to end	Day	19% 21% 37% 19% 4	297
February	1st to 10th	Day	23% 18% 35% 21% 3	270
	11th to 20th	Day	21% 22% 31% 19% 6% 1	270
	21st to end	Day	23% 19% 37% 19% 2	225
March	1st to 10th	Day	17% 20% 45% 16% 3	270
	11th to 20th	Day	28% 18% 32% 17% 4 1	270
	21st to end	Day	29% 16% 31% 19% 5%	417
April	1st to 10th	Day	17% 14% 39% 20% 10% 1	428
	11th to 20th	Day	21% 16% 29% 21% 13%	412
	21st to end	Day	23% 14% 35% 20% 8% 1	420
May	1st to 10th	Day	18% 13% 31% 27% 9% 1	423
	11th to 20th	Day	17% 9% 28% 27% 16% 3	598
	21st to end	Day	12% 5% 28% 31% 17% 6%	679
June	1st to 10th	Day	9% 6% 20% 31% 25% 9%	630
	11th to 20th	Day	9% 3 20% 36% 25% 7%	630
	21st to end	Day	4 6% 26% 36% 22% 6%	630
July	1st to 10th	Day	10% 2 12% 28% 33% 15%	621
	11th to 20th	Day	6% 3 16% 38% 29% 8%	618
	21st to end	Day	9% 3 16% 33% 30% 9%	684
August	1st to 10th	Day	8% 2 14% 37% 29% 11%	622
	11th to 20th	Day	12% 2 13% 29% 32% 12%	439
	21st to end	Day	9% 2 13% 28% 35% 13%	495
September	1st to 10th	Day	14% 3 14% 30% 30% 10%	450
	11th to 20th	Day	8% 3 13% 30% 32% 14%	450
	21st to end	Day	7% 8% 21% 28% 26% 10%	446
October	1st to 10th	Day	11% 10% 23% 36% 16% 4	270
	11th to 20th	Day	15% 17% 31% 27% 9%	270
	21st to end	Day	32% 16% 25% 19% 7%	297
November	1st to 10th	Day	12% 10% 33% 28% 13% 4	270
	11th to 20th	Day	19% 19% 28% 21% 13% 1	270
	21st to end	Day	23% 16% 27% 24% 9% 1	270
December	1st to 10th	Day	13% 19% 39% 19% 7% 3	270
	11th to 20th	Day	19% 16% 34% 26% 4	270
	21st to end	Day	24% 21% 39% 13% 4	297
January	1st to 10th	Night	17% 15% 38% 24% 5%	950
	11th to 20th	Night	21% 17% 35% 22% 4	950
	21st to end	Night	19% 14% 39% 26% 2	1045
February	1st to 10th	Night	22% 12% 38% 25% 3	950
	11th to 20th	Night	19% 14% 39% 26% 2	762
	21st to end	Night	21% 15% 40% 23% 2	628
March	1st to 10th	Night	19% 15% 39% 23% 4	751
	11th to 20th	Night	22% 11% 34% 27% 5%	570
	21st to end	Night	23% 12% 33% 26% 6%	627
April	1st to 10th	Night	15% 13% 38% 27% 7%	546
	11th to 20th	Night	16% 12% 34% 28% 10%	533
	21st to end	Night	20% 10% 37% 26% 6%	540
May	1st to 10th	Night	16% 6% 34% 34% 9%	540
	11th to 20th	Night	17% 5% 28% 32% 17% 1	531
	21st to end	Night	10% 3 24% 39% 20% 3	584
June	1st to 10th	Night	8% 2 20% 41% 28% 1	540
	11th to 20th	Night	7% 2 18% 49% 22% 1	540
	21st to end	Night	6% 1 24% 44% 24% 2	540
July	1st to 10th	Night	10% 1 8% 40% 34% 7%	525
	11th to 20th	Night	5% 2 15% 42% 33% 3	522
	21st to end	Night	6% 1 15% 40% 35% 2	591
August	1st to 10th	Night	7% 2 10% 42% 36% 3	537
	11th to 20th	Night	7% 1 13% 41% 35% 4	534
	21st to end	Night	6% 1 12% 39% 38% 4	594
September	1st to 10th	Night	13% 2 13% 37% 29% 6%	540
	11th to 20th	Night	9% 4 13% 34% 35% 5%	544
	21st to end	Night	9% 5% 23% 33% 26% 5%	720
October	1st to 10th	Night	10% 5% 26% 33% 23% 3	720
	11th to 20th	Night	17% 10% 29% 33% 11%	720
	21st to end	Night	22% 12% 31% 28% 6% 1	792
November	1st to 10th	Night	13% 8% 35% 32% 12% 1	740
	11th to 20th	Night	16% 14% 34% 29% 7%	760
	21st to end	Night	22% 10% 34% 27% 6%	831
December	1st to 10th	Night	21% 12% 35% 27% 5% 1	950
	11th to 20th	Night	23% 9% 29% 32% 6% 1	950
	21st to end	Night	25% 15% 34% 24% 2	1045

Page generated at 2024-03-31 05:08:54. Version ac07

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